(1) Field of the Invention
This invention relates to equipment and a method for manufacturing a Hgxe2x80x94Cdxe2x80x94Mnxe2x80x94Te based single crystal.
(2) Related Art Statement
Recently, attention has been paid to an erbium doped fiber amplifier. The wavelength of 0.98 xcexcm is particularly expected to be an exciting wavelength for erbium. The bulky Hgxe2x80x94Cdxe2x80x94Mnxe2x80x94Te based single crystal is much expected as a material for an optical isolator with a wavelength of 0.98 xcexcm band. The range of a composition usable for an optical isolator is described in JP-A 7-233000, for example.
In the past, it has been difficult to grow a bulky Hgxe2x80x94Cdxe2x80x94Mnxe2x80x94Te based single crystal using the Bridgeman process without breaking the crucible because of the high vapor pressure of Hg, which invariably raises the internal pressure within a crucible to such an exent as to cause breakage of the crucible.
JP-A 7-206598 describes equipment using a high pressure Bridgeman furnace, by which a Hgxe2x80x94Cdxe2x80x94Mnxe2x80x94Te single crystal is formed. The equipment has a heater above a crucible over the high pressure Bridgeman furnace to prevent the precipitation of Hg with higher vapor pressure in the crucible. JP-A-8-40800 discloses a method for setting a material of single crystal in a container so that in THM method (traveling heater method), the production of a twin crystal may be prevented and the diameter of the thus obtained single crystal may be made large.
Although the mass production of single crystals with large diameters is known, along with the ability to prevent generation of a twin crystal, a difficult problem remains unsolved: Manufacturing a single crystal with a large diameter at a relatively low cost. This is because the vapor pressure of Hg increases in geometrical progression as its diameter becomes large, so that a high pressure Bridgeman furnace is used, and a container for forming the single crystal is required to be pressurized at about 30 kg/cm3.
Compositional segregation is, however, recognized in the single crystal, as viewed in its diametrical direction, and sometimes crystals with different phases are generated since a melt has differing states between the outer peripheral part and the center part. Thus, since the characteristics of such a single crystal as an optical isolator largely vary, it is difficult to obtain one single crystal satisfying the characteristics required of an optical isolator. Moreover, the optical loss character of the isolator varies due to the deviation in the crystal orientation of the single crystal.
It is an object to improved and stabilize the characteristics of a single crystal.
It is a further object to enable the mass production of single crystals by prohibiting a compositional segregation, generation of different phases, deviation in the crystal orientation, etc., in the single crystal.
It is yet another object to provide manufacturing equipment for producing the single crystal.
This invention relates to equipment for producing a single crystal in each of a plurality containers of thermally treating a raw material for the single crystal in each of the containers, said equipment comprising heaters corresponding to each of the containers, an elevator to move each of the containers up or down relative to each of the respective heaters, and a connecting member to connect at least one of the container and the heater of each of the plurality of sets of containers and heaters mechanically to the elevator, wherein each container is moved vertically relative to each respective heaters by driving the elevator and passing it through an area of thermal treatment formed by the heater to continuously form a melt in the raw material inside the container, the single crystal being continuously produced in the container by solidifying the melt.
This invention also relates to a method for producing a single crystal in each of a plurality of containers by thermal treating of each container filled with sources of the single crystal, said method comprising thermal treating equipment corresponding to each container, an elevating drive to move each container up or down relative to each respective thermal treating equipment, and connecting members to connect at least one of the plurality of containers and the plurality of the thermal treating equipment mechanically to the elevating drive equipment, wherein each container is moved up or down relative to each respective thermal treating equipment by driving the elevating driving equipment and passing it through an area of thermal treatment formed by the thermal treating equipment to generate melting zones in the sources of the container in succession, and generating in each a single crystal container in succession by making the melting zones solid.
The present inventors have found that in the Hgxe2x80x94Cdxe2x80x94Mnxe2x80x94Te single crystal, for example, if the diameters of the single crystal and its container are increased, it is difficult to control microscopic compositional segregation, generation of different phase of crystals and deviation in the crystalline orientation are likely to occur. Based on the above finding, the inventors made further investigations. During their investigation, they tried to mass-produce single crystals by decreasing the diameters of the single crystal and the container to be filled with a starting material for the single crystal and increasing the number of the containers to be thermally treated.
Contrary to the expectations, in bundling a plurality of sealed members and setting them in a single THM furnace, it is very hard to control the characteristics of the single crystals in the many containers, thereby leaving the above-noted problems unsolved. That is, the condition of the each single crystal produced varies depending upon the respective containers. For example, in the case that a single crystal having good characteristics usable for an optical isolator is produced in one container, compositional segregation and different phase of crystals often occur in the single crystals in the other containers and the crystalline orientation is deviated among the single crystals. This means that it is very difficult to control a melt finely in each container in the case of treating many containers with their small diameters as well as in the case of the single crystals with large diameters. Moreover it is possible to bundle three to four sealing members at the maximum, but not possible to simultaneously grow single crystals for not less than five containers.
The inventors attempted to solve these fatally serious problems from the viewpoint of mass-production. During the studies, they have discovered that continuous production of the single crystals by providing heaters corresponding to respective containers, connecting each of the heaters mechanically to an elevator, vertically moving each of the heaters relative to the respective one of containers by driving the elevator, continuously producing a melt in the starting material for the single crystal by passing each container through an area for thermal treatment formed by the heater, thereafter solidifying the melt solves the above-noted problems.
Thus, they found that in each of the containers, the compositional segregation of the single crystals and the generation of different phases of crystals was prohibited and, also, that the fluctuations in the crystalline orientation in the single crystal were not observed. Accordingly, even in the single crystal for which it is difficult to control the melt such as a Hgxe2x80x94Cdxe2x80x94Mnxe2x80x94Te based single crystal, the present invention enables the mass production of single crystals beyond a certain level without causing compositional segregation, generation of different phase of crystals, or deviations in the crystalline direction.
The inventors further paid attention to the inner diameter of the container for growing the single crystal in developing equipment which enables the mass-production of the single crystal, and have also found that by setting the inner diameter of the container to 7 mm or less, the single crystal having a desired composition within a particular range can be mass-produced for the weight of the starting material. If the diameter is greater than 8 mm, the composition largely differs between an outer peripheral part and a central part of the single crystal, thereby giving a low yield during the growing step of the single crystal. However, by setting the inner diameter of that area of the container in which to grow the single crystal to 7 mm or less, the yield can be remarkably enhanced.
The reason for this is that the heat conduction from the heater is increased to stabilize the condition of the melt successively produced in the polycrystalline starting material and thus suppress different phase of crystals and the compositional segregation.
Preferably, the inner diameter of the container is 5 mm or less, and more preferably 3 mm or less. The lower limit of the inner diameter is only required to be larger than the dimension of the product to be manufactured.